Several methods are known for analyzing chemical compounds, including mass spectrometry (MS), gas or liquid chromatography (GC or LC), and nuclear magnetic resonance imaging (NMR). Each of these methods requires the user to introduce a chemical compound to the apparatus used to perform the chemical analysis. The following is a brief description of these apparatus and methods, which description is not intended to be comprehensive, or to limit in any way the application of the compounds and methods described herein. A more detailed description of these analytical methods may be obtained from the contemporary scientific literature. Moreover, those skilled in the analytical chemistry arts will be familiar with these methods and the apparatus used to perform these methods.
For example, mass spectrometry involves the analysis of ionized analytes in a gas phase using an ion source, a mass analyzer that measures the mass-to-charge (m/z) ratio of the ionized analytes, and a detector that registers the number of ions at each m/z value. The MS apparatus may also be coupled to a separation apparatus to improve the ability to analyze complex mixtures. Further, MS instrument combinations can be made to enhance sensitivity and selectivity. Regarding ion source, electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) are two commonly used techniques to ionize the chemical compounds for analysis. ESI ionizes the analytes from a solution and, depending on the ionization method, may result in either negatively or positively charged ions. MALDI desorbs and ionizes the sample using a “matrix” that encourages desorption and ionization when exposed to light energy.
There are several types of mass analyzers, including ion trap, time-of-flight (TOF), quadrupole (Qq) magnetic sector, and Fourier transform ion clyclotron (FT-MS) analyzers, each varying in analysis characteristics. These analyzers may be run separately or assembled in tandem to maximize sensitivity and strengths of MS analysis. For example, MALDI is usually coupled to a TOF analyzer, but may also be coupled to quadrupole ion-trap and to combined TOF instruments or FT-MS. For example, in TOF-TOF, two TOF sections are separated by a collision cell. In the hybrid quadrupole TOF apparatus, the collision cell is placed between a quadrupole mass filter and a TOF analyzer. These examples illustrate how “tandem” mass spectrometry apparatus may be assembled from intact MS apparatus or selected components of the instruments. The design of the tandem MS instrument allows versatility and increased sensitivity depending on the goal of the analysis and the chemical composition of the analyte.
Chromatography involves separation of molecules based on differences in their structure and/or composition. In general, chromatography involves moving a sample of the materials to be separated over a stationary support. The molecules in the sample will have different interactions with the stationary support leading to separation of similar molecules. Test molecules which display tighter interactions with the support will tend to move more slowly through the support than those molecules with weaker interactions. In this way, different types of molecules can be separated from each other as they move over the support material.
Chromatographic separations can be carried out using a variety of supports, including immobilized silica on glass plates (thin layer chromatography), volatile gases (gas chromatography), paper (paper chromatography), and liquids which may incorporate hydrophilic, insoluble molecules (liquid chromatography).
A gas chromatograph includes three major components: an analytical column that physically separates the components of the mixture, a detector that senses the individual component after separation, and an injector that introduces the gas sample and carries the sample to the analytical column by carrier gas.
Nuclear magnetic resonance (NMR) is a physical phenomenon involving the interaction of atomic nuclei placed in an external magnetic field with an applied electromagnetic field oscillating at a particular frequency. Magnetic conditions within the material are measured by monitoring the radiation absorbed and emitted by the atomic nuclei. NMR is used as a spectroscopy technique to obtain physical, chemical, and electronic properties of molecules.
In NMR, the sample to be tested is placed in a static external magnetic field. An antenna (usually a coil-shaped inductor with the sample inside) is used to irradiate the sample with radio waves. At certain frequencies, atomic nuclei within the sample will absorb the radiation and enter an excited state. After a time, the nuclei will re-emit the radiation, which can be detected by the antenna. Finally, a measurement is taken of how much radiation is re-emitted, and when. Only nuclei with non-zero magnetic moment can undergo NMR.
Highly reactive materials, such as organometallic halides, present several problems when attempts are made to perform MS, chromatographic, NMR, or other chemical analyses on them. In particular, these materials are highly reactive to many of the tools currently employed in chemical analysis. For example, many organometallic halides will react rapidly with rubber, glass, and other oxides upon injection into a gas chromatograph, or when used in glass capillaries used in electrospray mass spectrometry, resulting in erroneous analysis results when the instrumental data output is examined.
In addition, many of the organometallic halides will readily hydrolyze when they are placed in an aqueous buffer media, which may be used in electrospray MS, thereby leading to flawed measurement results. These materials may also be difficult to ionize, also leading to difficulties when they are being analyzed using electrospray MS.
One class of organometallic halides—organochloro silanes—is used extensively for surface coatings, to add lubricity, and for other purposes. Organochloro silanes are used, for example, to create hydrophobic coatings for analytical instruments, such as protein arrays, DNA arrays, and gas and liquid chromatograph columns. They are also used as protective coatings on windshields, and as lubricants on magnetic media such as disk drives. For many of these applications, it is useful to perform some chemical analysis, such as MS, LC or GC, or NMR, prior to forming the coatings in order to confirm the identity of the organochloro silane being used.
Therefore, there exists a need for methods and compounds that are useful to facilitate the analysis of organometallic halides by mass spectrometry, gas or liquid chromatography, nuclear magnetic resonance imaging, and other methods that require the use of equipment with which the organometallic halides might react.